Hitherto, some image forming apparatuses such as a copier, a laser beam printer, a facsimile machine, and a multi-function printer are provided with a sheet processing apparatus configured to carry out such a process as stapling on sheets on which images have been formed. Such a sheet processing apparatus is configured to bind a sheet bundle by using a metallic staple. Such a stapling process using the staple is adopted in many sheet processing apparatuses because it enables to bind a plurality of output sheets reliably at a position specified by a user.
However, it is necessary, and hence troublesome, to remove the staple in putting the stapled sheets through a shredder. It is also necessary and troublesome to remove the staple to separate the sheets and the staple in recycling the stapled sheet bundle from an aspect of environmental concerns.
Due to that, Japanese Patent Application Laid-open No. 2010-189101 proposes a sheet binding apparatus provided with a pair of die members having concave and convex teeth. This sheet binding apparatus binds a sheet bundle by entangling fibers of the overlapping sheets with each other by forming concave and convex portions on the sheet bundle in a thickness direction thereof by engaging the pair of die members after stacking and aligning the sheets. That is, this sheet binding apparatus binds the fibrous sheets without using staples.
However, such a sheet binding apparatus is liable to cause such a problem that the sheet is torn and paper powder thereof attaches on the teeth of the die members if the sheet bundle on the way of the binding process is forcibly pulled and taken out due to such a reason of jamming of a sheet.
Still further, if a number of times of the binding process increases, the paper powder generated during a fastening process may accumulate between the teeth of the pair of die members. If the paper powder attaches on the teeth or accumulates between the teeth as described above, there is a possibility that the paper powder affects the engagement of the upper and lower dies in executing a next binding process and drops a fastening power of the sheet bundle that has been bound.